update regexp to include options for nearby and multiline search types

regex engine user docs: https://gitlab.com/bytesweep/bytesweep-worker/blob/master/REGEX.md

regex rule file: https://gitlab.com/bytesweep/bytesweep-worker/blob/master/regex.yaml

nearby source: https://gitlab.com/bytesweep/bytesweep-worker/blob/master/modules/strings.py#L66-94

multiline source: https://gitlab.com/bytesweep/bytesweep-worker/blob/master/modules/strings.py#L96-125